Method of producing adhered substrates

ABSTRACT

A method of producing adhered substrates that includes: providing an adhesive composition that is a liquid dispersion when stored at temperatures from about room temperature up to about 140° F., becomes a molten solution when heated to a temperature above about 300° F. and mixed, and then becomes a non-exuding thermoplastic solid adhesive upon cooling below a temperature of about 140° F.; heating and mixing the liquid dispersion at a temperature above about 300° F. to form the molten blend; disposing the molten blend between the substrates to be adhered to each other; and retaining the molten blend between the substrates to be adhered to each other for a set time during which the molten blend cools to form the solid adhesive that adheres the substrates to each other.

RELATED APPLICATIONS

This application is a continuation of application Ser. No. 10/629,876,filed Jul. 29, 2003, now U.S. Pat. No. 7,285,583, and claims thebenefit, under 35 U.S.C. §119(e), of: U.S. Ser. No. 60/399,535, filedJul. 30, 2002; U.S. Ser. No. 60/412,907, filed Sep. 23, 2002; and U.S.Ser. No. 60/433,840, filed Dec. 16, 2002.

FIELD OF THE INVENTION

The invention relates to adhesive compositions and, more specifically,to a hybrid plastisol/hot melt composition especially suited as anadhesive for packaging and the like.

BACKGROUND OF THE INVENTION

Hot-melt adhesives are adhesives which are solid at room temperature andwhich are applied to the substrates to be joined in the form of a melt,solidifying on cooling after the substrates have been joined together.In the case of thermoplastic adhesives, this operation can be repeatedindefinitely because they do not cross-link. They are essentially basedon polymers, such as polyamides, polyesters or polyolefins. Thesepolymers typically determine the properties of the adhesive layer inregard to adhesion, strength and temperature behavior. In order toobtain special properties for specific applications, additives areincorporated, for example tackifiers to increase adhesion, plasticizersto increase flexibility, waxes to shorten the open time orcrystallization accelerators to improve morphology.

Hot melt adhesives are used widely in the packaging industry for suchapplications as case and carton sealing, tray forming and box forming.The substrates to be bonded include virgin and recycled kraft, high andlow density kraft, chipboard and various types of treated and coatedkraft and chipboard. Composite materials are also used for packagingapplications such as for the packaging of alcoholic beverages. Thesecomposite materials may include chipboard laminated to an aluminum foilwhich is further laminated to film materials such as polyethylene,MYLAR, polypropylene, polyvinylidene chloride, ethylene vinyl acetateand various other types of films. Additionally, these film materialsalso may be bonded directly to chipboard or kraft. The aforementionedsubstrates by no means represent an exhaustive list, as a tremendousvariety of substrates, especially composite materials, find utility inthe packaging industry.

It would be advantageous to provide a non-PVC adhesive composition thatwas a liquid at room temperature, a hot-melt solution at elevatedtemperatures, and a solid adhesive upon cooling.

For certain packaging and related applications, it may further bedesirable to provide an adhesive that meets as many of the followingtechnical specifications as possible: liquid at room temperature; stableover long periods (at least one year); chlorine free; low volatility;easily pumped by gravity feed to a gear or piston pump; largelyunaffected by storage at 140 degrees F.°; low cost; ready to use asreceived (no mixing); will not “pack out,” separate, or change whenpumped or pressurized; fuses to become a molten adhesive at elevatedtemperatures; FDA approved for indirect food contact; has good heatstability at fusion temperature; melt viscosity <10,000 cps; T_(g)similar to conventional EVA packaging grade hot melts; open molten timeof about 7 seconds when applied at 350 degrees F.°; set time aftercompression between two substrates of about 2 seconds; capable ofproducing fiber tear adhesion to clay coated printed paperboard;foamable to a 50% density reduction while maintaining other adhesionspecifications; and able to be compounded with up to 30 phr filler.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to a liquid plastisol/hot melt hybrid adhesivetechnology that has been developed based on a blend of functionallyspecific materials. The adhesive is in the form of a liquid dispersionat room temperature, and is stable as a liquid when stored attemperatures of up to approximately 140° F. The liquid adhesive isdesigned to fuse and melt when the dispersion is exposed to temperaturesin excess of 300° F. With adequate mixing, the dispersed ingredientsform a soluble, molten “hot-melt” solution, which can be dispensed likeother hot melt adhesives onto various substrates for industrial adhesiveand packaging applications. Once dispensed, the molten hot melt cools toform a solid adhesive which is capable of producing fiber tear whenadhered to common clay coated paper stock.

The hot melt may be thermally stable for periods in excess of five hoursat process temperatures, and like other thermoplastic adhesives, it canbe remelted, and reused after cooling. The achievement of fiber tearadhesion is strongly dependent on mixing (since there are two polymercomponents), and on activation temperature. Inadequate mixing willresult in cohesive failure of the adhesive. Similarly, the adhesive ispreferably molten and mixed at temperatures in excess of 350° F. toactivate the chemistry; otherwise, the adhesive may cohesively fail.

The adhesive compositions of the invention are based on blends ofmaterials, each of which is dispersed as particulates within a liquidvehicle. Unique processes for mixing and applying the adhesivecompositions have also been developed. The particulates are chosen basedon their ability to impart a specific function in the finished adhesive,and on their ability to resist liquid adsorption at storagetemperatures. More specifically, it has been discovered that theplastisol/hot melt hybrid of this invention contains a liquid phase,which serves as the vehicle for dispersion of the ingredients; areinforcing phase, which gives the adhesive the requisite cohesivestrength for the end use application; and an adsorbent phase, whichprevents exudation of the liquid phase during hot melt processing,during application, and during end-use. The adhesive compositions alsopreferably include an activator, which activates the chemistry and helpsto prevent exudation in the finished product; a thermal stabilizer,which provides thermal stability at process temperatures; and secondaryadditives (optional) for the purpose of controlling viscosity, cost, settime, foaming, etc. The adhesive compositions of the inventionpreferably do not contain polyvinyl chloride (“PVC”).

In a particularly preferred embodiment, the liquid phase is comprised ofmineral oil; the reinforcing phase is comprised of eitherpoly(ethylene-co-vinyl acetate), a poly(ethylene-co-vinylacetate-co-methacrylic acid)terpolymer, a poly(ethylene-co-vinylacetate-co-maleic anhydride)terpolymer, or a mixture thereof; theadsorbent phase is comprised of poly(propylene-co-maleic anhydride),either alone or mixed with other ingredients such as a polypropylenehomopolymer, a tackifier such as a rosin ester of pentaerythritol, or amixture thereof; the activator is comprised of a dicarboxylic acid suchas sebacic acid or dodecanedioic acid; the thermal stabilizer iscomprised of a mixture of Irganox 1010 (a hindered phenol), and IrganoxPS800 (dilauryl thiodipropionate) from Ciba; and the optional secondaryadditives are comprised of one or more components, including but notlimited to materials such as a clay filler, carbon black, an inorganicor organic pigment, a foaming agent such as azobisdicarbonamide, afoaming agent catalyst such as zinc oxide, or any combination thereof.

In a further preferred embodiment, the ratios of the ingredients arecontrolled so that the reinforcing phase is in excess of the adsorbentphase. In this way, sufficient cohesive strength is maintained, andliquid exudation is prevented in the finished product.

In yet another embodiment, cohesive strength and stiffness are furtherenhanced through the incorporation of nanoparticles, where it has beenfound that the method of mixing these particles is important to theachievement of optimum properties. In one scenario, nanoparticleaggregates are exfoliated in the hot-melt molten state, while in asecond scenario, they are pre-exfoliated in the dispersion state. In thefirst scenario, nanoparticle aggregates are added to the dispersion withlittle to no change in the dispersion state viscosity. The aggregatesare then exfoliated during the melt-processing stage to yield a truenanocomposite adhesive. The advantage of this scenario is that theliquid dispersion can be easily prepared through simple low shearmixing. Also, the resultant dispersion is relatively low in viscosity,and as such is it easily processed as a liquid (i.e., through pumping,pouring, etc.). In the second scenario, the aggregates are purposelypre-exfoliated (either partially or completely) in the dispersion stateto yield a mixture with controllable rheological characteristics rangingfrom those of a liquid to those of a gel—independent of the organicingredient concentrations. The advantage of this scenario is that thedispersion can be processed in applications where higher viscosities arerequired (with no change in the chemical composition). However,regardless of which scenario is employed, enhanced physical propertiesare only achieved when the nanoparticle aggregates are exfoliated in thefinished solid adhesive.

The overall ratio of liquid to polymer is also controlled so as tomaintain a balance between storage stability, hot melt viscosity, andcohesive strength of the finished product. Generally, higher levels ofliquid necessitate the use of higher levels of the adsorbent phase (toprevent exudation), which diminishes the cohesive strength of theadhesive. A minimum level of activator (diacid) may be required to bothprevent exudation, and to activate the chemical component of theadhesive. Surprisingly, the activator has no effect in the absence ofthe adsorbent phase.

It is important to note that in combination, these components act in asurprising synergy to form a liquid plastisol/hot melt hybrid adhesive.The omission of any essential ingredient will result in diminishedadhesive performance. Furthermore, the synergy can only be realized withadequate mixing of the materials, and with adequate activation of thechemistry; both of which depend on the method(s) of processing andapplication.

In general, the liquid phase enables the composition to be packaged as aliquid at room temperature, which is a unique and desirable aspect ofthis invention. The choice of liquid may be limited by severalconstraints including cost, compatibility with the adsorbent phase,volatility at both elevated temperatures (during processing) and atend-use temperatures, and acceptability for indirect food contactapplications. In one especially preferred embodiment of this invention,mineral oil comprises the liquid phase. However, depending on theapplication, the liquid phase can be any low volatility liquid compound,as long as it is compatible with the adsorbent phase in the finishedformulation. Such liquids can be either reactive (e.g., acrylic, epoxy,isocyanate-based materials, trialkoxysilane and hydrolyzed and/oroligomerized products thereof, acid functional compounds like isostearicacid); or non-reactive (e.g., aliphatic hydrocarbons, hydrocarbon estersof diacids like adipic, sebacic, and phthalic acid, esters of monoacids,esters of natural fatty acids such as methyloleate, glyceroldioleate,vegetable oils such as soy oil, epoxidized soy oil, etc.), orcombinations thereof. If the reinforcing phase and the adsorbent phaseare of higher polarity, then other liquids could include water,glycerol, ethylene glycol, propylene glycol, and mixtures, etc. Ifreactive liquids are employed, photo and thermal initiators can be usedto crosslink the liquids either during the processing of the finishedproduct, or after thermoforming (in which case a photoinitiator, orhigher temperature decomposing thermal initiator could be used to finishthe cure).

The reinforcing phase provides the finished adhesive with its mechanicalintegrity, and as such it must have the ability to fuse, melt, andquickly cool to become a solid after it is applied to a substrate. Ithas been discovered that polymeric materials such as polyolefins arebest suited for this purpose. In a preferred embodiment, a polymericreinforcing phase preferably exists in the form of discrete particlesthat are dispersed in the liquid phase at room temperature. It isimportant that the particles do not adsorb the liquid at temperaturesbelow 140° F. In this way, the stability of the liquid adhesive ismaintained both during storage and during shipping.

When the dispersion is heated, the polymeric particles (which willcomprise the reinforcing phase in the finished adhesive) fuse with theliquid phase to form a molten blend. The temperature of fusion isdictated by the rheological characteristics of the polymer in thepresence of the liquid. These characteristics are controlled by severalvariables including polymer molecular weight, copolymer composition,solubility with the liquid phase, solubility with the other ingredients,and the composition ratios of all ingredients.

It has been further discovered that in order for the adhesive to havethe desired end-use properties, the reinforcing polymer phase should bemiscible with both the liquid and adsorbent phases at elevatedprocessing temperatures (i.e., in the fused, molten state).Incompatibility at elevated process temperatures can result inincomplete mixing, exudation of the liquid, and exudation of the otheringredients; all of which can interfere with adhesion to the substrate,and can deter from the end-use performance properties.

Further, it has been surprisingly found that the liquid phase should notbe completely compatible with the reinforcing phase upon cooling.Although partial compatibility is acceptable, it is more desirable forthe liquid phase to separate from the reinforcing phase upon cooling.This counterintuitive finding stems from the observation that if theliquid is too compatible, the mechanical strength of the resultantadhesive is decreased, the “set time” for the hot melt becomesexceedingly long, and the shelf stability of liquid dispersion iscompromised. It is most desirable for the reinforcing phase polymer tobe incompatible with the liquid phase at temperatures below 140° F. (tomaintain storage stability of the liquid dispersion), and to becompatible with the liquid phase at higher temperatures. The balancebetween compatibility at elevated temperatures and incompatibility atstorage temperatures depends on the solubility of the liquid in thereinforcing phase, which in turn depends on copolymer composition, thechoice of polyolefin, the choice of liquid, and the ratio of theingredients.

In one especially preferred embodiment of this invention, thereinforcing phase is comprised of a poly(ethylene-co-vinylacetate)polymer (EVA). However, the reinforcing phase could conceivablybe any polyolefin copolymer or terpolymer (linear, graft, or block) aslong as it meets the criteria described above. Such polymers can includecopolymers prepared with monomers of ethylene, butylene, propylene orbutadiene, etc; copolymerized with other monomers such as vinyl acetate,methyl acrylate, methyl methacrylate, butyl acrylate, styrene (likeIndex™ polymers from Dow, and Kraton™ polymers from Shell), maleicanhydride, maleic acid, acrylic acid, methacrylic acid, vinyl methylether, glycidyl ethers, trimethylolpropanemonoallylether, vinylchloride, etc. The reinforcing phase could also be comprised of higherpolarity polymers such as polyvinyl alcohol and its copolymers(polyvinylbutyral, polyvinylformal, ethylene vinyl alcohol), polyamides(nylons), and polyvinylpyrrolidone copolymers. It can be appreciatedthat acid, alcohol, or anyhydride functional polymers can enhanceadhesion to multiple substrates, and can also provide the capacity tochemically react with a reactive liquid phase and/or adsorbent phase ifso desired.

In addition, thermally activated curing agents can be incorporated tocross-link the reinforcing phase and/or the adsorbent phase so as tofurther improve the physical properties of the finished adhesive. Thethermosetting embodiment of the present invention can be achieved viamany conventional chemical pathways (familiar to those skilled in theart), one example of which may include the use of a thermally activatedperoxide additive such as t-butylperoxide in combination with anethylene copolymer as the reinforcing phase. The curing agent could alsobe chosen so as to not react at the temperatures required for mixing andapplication, but instead to react in either a post-thermal curingprocess, in a post UV/visible light activated process, or in amoisture-activated curing process step. These embodiments could befurther formulated to make useful coatings and sealants for metals,wood, plastic, and the like.

It can be further appreciated that blends of the aforementioned polymerscan be employed, where blending can either be accomplished throughphysical mixing of polymers followed by pulverizing into powder form; orthrough the polymerization process as would be accomplished in acore-shell emulsion or dispersion polymerization. For example, acore-shell emulsion or dispersion process could be used to produce acore of the desired composition for end-use mechanical properties (likea terpolymer of polyethylene-co-vinylacetate-co-methacrylic acid with aVA content of greater than 15%), and a shell which provides shelfstability when the particles are dispersed in the liquid phase of theinvention (like a copolymer of ethylene and vinylacetate where the VAcontent is less than 9%). The shell could also be comprised of theadsorbent phase for the system (as long as shelf stability can bemaintained during the storage of the dispersion).

Although incompatibility between the liquid and the reinforcing phase isa prerequisite for attaining a desirable level of cohesive strength inthe finished adhesive, it has been observed that exudation of the liquidfrom the fused solid leads to interfacial adhesive failure. For example,a fused and molten composition of EVA with mineral oil cools to form apolymer with the requisite toughness, but exudation of the oil uponcooling interferes with the adhesive's ability to form a long lastinginterfacial bond with the substrate.

It has been found that like EVA, polypropylene homopolymers andcopolymers are capable of fusing with mineral oil to form soluble moltencompositions at elevated process temperatures; but unlike EVA, thesecompositions remain surprisingly compatible upon cooling to temperaturesbelow 140° F. (as evidenced by minimal to no exudation of liquid fromthe blends after cooling). Although polypropylene and its copolymers aremore compatible with the liquid phase than EVA (a positive benefit forminimizing liquid exudation in the finished adhesive), this sameattribute deteriorates the resultant cohesive strength, making thesepolymers poor choices for the reinforcing phase. On the other hand, thissame “detrimental” attribute has been employed as an important aspect ofthe present invention. Namely, when polypropylene and/or its copolymersare melt-blended with EVA and mineral oil, they “adsorb” the oil in thecomposition, which otherwise would exude from the finished adhesive. Inthis way, the resultant blend displays the simultaneous characteristicsof improved strength (from the reinforcing phase), and minimal exudation(from the adsorbent phase). Thus, in blended form, these components worktogether in a surprising synergy to provide properties that could not beattained from either component alone.

Hence, this invention makes use of a reinforcing phase that must beaccompanied by an adsorbent phase to prevent exudation of liquid fromthe fused solid adhesive. In order to maintain the cohesive strength ofthe adhesive, the reinforcing and adsorbent phases must be employed at aratio where the reinforcing phase is in excess of the adsorbent phase.Otherwise, cohesive strength and interfacial adhesion are compromised.Like the reinforcing phase, the adsorbent phase polymers (or othermaterial) should be initially dispersed as particulates material intothe liquid phase, together with the dispersed reinforcing phase polymer.In this way, the adhesive can be stored and processed as a liquiddispersion (a desirable feature of this invention).

The composition of the adsorbent phase is also not limited to polymericmaterials. In fact, stearic acid has been shown to adequately performthis function. However, a copolymer of polypropylene with maleicanhydride has been found to be the preferred adsorbent phase material,either alone, or in combination with a polypropylene homopolymer. Forexample, although stearic acid is capable of preventing exudation, thissame attribute results in poor shelf stability at temperatures below140° F. This is because stearic acid melts and becomes compatible withthe mineral oil at a relatively low temperature. Thus, althoughparticulates of stearic acid can remain dispersed in mineral oil at roomtemperature for indefinite periods, the particulates prematurely gelwith the mineral oil at temperatures below 140° F. Surprisingly however,particles of polypropylene and its copolymers do not adsorb the mineraloil at storage temperatures, yet they help to prevent exudation of theliquid from the finished, solid product. These polymers also result inan adhesive composition with a greatly reduced set time, which can be animportant attribute for economic reasons. Thus, poly(propylene-co-maleicanhydride) and polypropylene enable the adhesive composition to displaygood liquid shelf stability, low exudation, and a fast set time.

The choice of adsorbent phase also depends greatly on the choice ofliquid (for reasons related to compatibility). In general, the adsorbentphase can be comprised of a polymeric material, a low molecular weightcompound, a high surface area inorganic material, or a combination ofthe three. Polymers can include relatively non-polar materials such aspolyolefins (like polypropylene and its copolymers, polyethylene and itscopolymers, polystyrene copolymers); or relatively polar polymers likenylon, polycaprolactone, polyvinyl alcohol and its copolymers, etc.Other resinous materials can include higher molecular weight aliphatichydrocarbon waxes, esters, terpene resins, and rosin esters likepentaerythritol ester of tall oil rosin, etc. Low molecular weightcompounds can include materials that are capable of gelling with theliquid phase like the aforementioned stearic acid, or like othersincluding azelaic acid, benzoic acid, stearic acid, citric acid,tartaric acid, biotin, niacin, etc. The adsorbent phase can also includetraditional micron-sized inorganic fillers, or high surface areainorganic materials, especially nano materials with surface areas inexcess of 30 m²/g, and more preferably 100 m²/g and higher. Suchnano-materials can be surface treated with compounds that furtherenhance their ability to adsorb the liquid phase. Surface treatments caninclude organosilanes such as n-octyltriethoxysilane, monoacids likestearic acid, quaternary ammonium compounds, or others.

In cases where the adsorbent phase is organic (polymers or low molecularweight compounds), the upper storage temperature limit of the liquiddispersion appears to be related to the melt temperature of theadsorbent phase material, and to the compatibility of the liquid phasewith the molten product. Polypropylene (PP) homopolymer has a highermelt temperature than that of its copolymers, and thus the upper storagetemperatures for compositions with a PP adsorbent phase will be thehighest. However, acceptable adhesion is only achieved when a PPcopolymer is employed, either alone, or in combination with PPhomopolymer, where maleic anhydride is the preferred comonomer in thecopolymer composition. It is believed that this is in part due to theability of the maleic anhydride groups to provide reactivefunctionality, which can facilitate the bonding of the adhesive to thesubstrate. In addition, better cohesive strength is achieved when theadsorbent and reinforcing phases are partially compatible, and whencompared to PP homopolymer, PP copolymers are more compatible with EVA.

In another embodiment, the adsorbent phase material, the liquid phasematerial, or both in combination can be comprised of components thatyield finished materials with excellent release characteristics. Such“release” components have the surprising capacity to prevent exudation(like their adhesion promoting counterparts), while enabling the solidmaterial to be easily peeled away from the substrate over which it isapplied. An example of an adsorbent phase material that suits thispurpose is N,N′-ethylenebisstearamide, while an example of a liquidphase material includes isostearic acid. Uses for this embodiment caninclude molded parts, or applications where temporary protectivecoatings are desired for metals, paper products, wood products, glassproducts, and others.

In addition to maleated PP, it has been surprisingly found that othercompounds can be added to the formulation to both minimize liquidexudation, and to enhance the performance of the adhesive. Althoughthese compounds do not prevent exudation by themselves (i.e., theycannot replace the adsorbent phase polymer), they functionsynergistically with the adsorbent phase to both deter exudation, and tolower the process temperature required for activation of the adhesive.The preferred “activators” for this invention are chosen from the classof dicarboxylic acid compounds. Other compounds capable of catalyzingthe ring opening of maleic anhydride (such as amine containingcompounds, water, etc.) could also be employed, either separately, or incombination with the dicarboxylic acid compounds. Such compounds couldbe aqueous-based, and as such they could be optionally dispersed in theoil phase with appropriate surfactants. Also, dicarboxylic acidcompounds could be neutralized and rendered water soluble for dispersionin the oil phase to form water-in-oil emulsions. However, the choice ofactivator, like the other ingredients, is limited by several constraintsincluding cost, compatibility with the other components, volatility atboth elevated temperatures (during processing) and at end-usetemperatures, and acceptability for indirect food contact applications.In one preferred embodiment of this invention, dodecanedioic acidcomprises the activator. In another preferred embodiment, sebacic acidcomprises the activator.

Interestingly, not all acids or mixtures of acids provide the beneficialattributes that are observed with either dodecanedioic acid or sebacicacid. For example, a mixture of dodecanedioic acid, sebacic acid, andundecanedioic acid (commercially available as Corfree™ from duPont) doesnot provide the synergistic benefit that is observed when eitherdodecanedioic acid or sebacic acid is used alone. This unpredictableresult adds further intrigue to the discovery that the addition ofeither dodecanedioic acid or sebacic acid results in faster set time,less exudation, better adhesion, and lower temperatures for adhesionactivation. Although not wishing to be bound by any single theory, it isbelieved that the diacids have the ability to react with the comonomerconstituents, and thus can both catalyze the ring opening of maleicgroups, and can graft onto the polymer. It has also been found thatthere is an upper limit of diacid beyond which no additionalimprovements are achieved.

In one preferred embodiment, the diacid compounds are dispersed in theliquid phase together with the other dispersed ingredients. It isimportant that the diacid particles do not become soluble in the liquidat temperatures below 140° F. In this way, the stability of the liquidadhesive is maintained both during storage and during shipping.

In addition to the aforementioned ingredients, the preferred formulationshould also contain a thermal stabilizer so that adequate processstability can be achieved. Two stabilizers that have been found to beadequate for this purpose include Irganox 1010 (a hindered phenol), andIrganox PS800 (dilauryl thiodipropionate) from Ciba. Both are generallyused at concentrations of <1% by weight of the polymeric materials inthe adhesive composition. It has also been found that fillers such asvarious clays and talcs can be added to the formula to reduce cost, andto further reduce the set time upon cooling. In addition, tackifierssuch as rosin ester derivatives and hydrocarbon-based derivatives canalso be added to reduce viscosity at process temperatures, and toimprove adhesion to certain substrates. Heat activated blowing agentssuch as azodicarbonomide and the like may also be used as additives tofoam the hot melt for the purpose of reducing density and cost.

In another embodiment, the aforementioned dispersion state ingredientscan be further mixed with inorganic nano-materials such asmontmorillonites (aluminum silicates), aluminum oxide and its hydrateforms, titanium dioxide, zinc oxide, iron oxide, etc. Nanoparticles havethe added benefit of increasing the modulus, the cohesive strength, andthe heat distortion temperature of the finished adhesive. However, suchimprovements are only realized when the nanoparticles are properly mixedand exfoliated in the finished solid adhesive. In a true nanocomposite,the nanometer-sized platelets have a major influence on the molecularconfiguration of the polymer chains (since the dimensions of ananoparticle are on the same scale as the dimensions of a polymerchain). An unperturbed polymer chain has a characteristic radius ofgyration that roughly depends on its molecular weight, and bondrotational barriers (stiffness). When conditions are favorable, thepolymer can adopt an extended chain configuration as it stretches outand adsorbs onto the nano-surface. This has the effect of raising bondrotational barrier energies, and making the chain stiffer. Consequently,macroscopic properties like modulus, toughness, diffusion, and heatdistortion are all affected. In a preferred embodiment, montmorillonitecan be exfoliated with the aforementioned dispersion ingredients in anycombination to form a nanocomposite adhesive. Aside from having a highermodulus, the nanocomposite also exhibits a higher heat distortiontemperature, and improved adhesion at elevated temperatures. The heatdistortion temperature increases by as much as 25° F. to 30° F. with aslittle as 3% to 6% montmorillonite by weight.

In order for all of the aforementioned composition ingredients toperform their intended functions, it has also been discovered thatmolten-state mixing is critical. For example, even though thecomposition is capable of providing an adhesive with the requisiteproperties for paper packaging applications, adhesion does not occurunless the materials are adequately mixed in the molten state. It hasbeen shown that after adequate molten state mixing, the adhesive coolsto form a solid, which in turn can be re-melted and used as atraditional hot melt adhesive. As such, the adhesive could be fabricatedinto solid pellets, which would render it useful with traditional hotmelt adhesive equipment if so desired. In addition, solidified pelletsor powders of the formulations encompassed by this invention could inthemselves be used as formulation additives for traditional, extrudedand/or pelletized, hot melt adhesives. As such, traditional hot meltscould reap the benefits of improved adhesion as well as enhancedphysical properties from exfoliated nanoparticles.

Although the solidified versions of the formulations encompassed by thisinvention are indeed useful and novel, the liquid nature of thisadhesive and its shelf stability are an especially advantageous aspectof the invention. In order to take advantage of this aspect of theinvention, it is conceivable that the adsorbent phase and reinforcingphase polymers could be premixed together with the remaining solidingredients (through melt or solution blending), pulverized, andsubsequently dispersed as particulates into a liquid medium. Likewise, aprocess could be employed that performs both the premixing function, andfacilitates the application of the molten, blended adhesive compositiondirectly onto the substrates that are to be adhered. In keeping withthis objective, an innovative method has been developed whichsimultaneously serves to both mix the composition (required foradhesion), and to apply it directly to the packaging substrate. Thus,when this method is employed, the adsorbent phase and reinforcing phaseparticulates can be added as discrete particles to the liquid phasedispersion (a preferred state of dispersion in the liquid adhesive).

In embodiments where it is desirable to further enhance cohesivestrength and stiffness with nanoparticles, it has likewise been foundthat the method of mixing is critical to the achievement of optimumproperties. In one preferred embodiment, nanoparticle aggregates areexfoliated in the hot-melt molten state, while in another embodiment,they are pre-exfoliated in the dispersion state. In the first scenario,nanoparticle aggregates are added to the dispersion with surprisinglylittle to no change in the dispersion state viscosity. The aggregatesare then exfoliated during the melt-processing stage to yield a truenanocomposite adhesive. This method offers a process advantage from thestandpoint that nanocomposite materials can be formed from relativelylow-viscosity liquid dispersions. Thus, when nanoparticles areincorporated as aggregates, they have little to no effect on viscosity,and no special process equipment is required to pump or mix the liquiddispersions. Instead, partial or complete exfoliation is accomplishedlater, through high shear mixing during the final application process.In the second scenario, the aggregates are purposely pre-exfoliated(either partially or completely) in the dispersion state to yieldcontrolled rheological characteristics ranging from those of a liquid tothose of a gel, independent of the organic ingredient concentrations.Exfoliation (either in the dispersion state or in the molten state) canbe achieved through any combination of methods, including those thatemploy high shear mixing, and/or ultrasound. Regardless of whichembodiment is employed, enhanced physical properties are only achievedwhen the nanoparticle aggregates are exfoliated (either partially orcompletely) in the finished solid adhesive.

It should be noted that that in addition to the adhesives of the presentinvention, other polymer solutions and dispersions can also benefit fromthe processing advantages of incorporating nanoparticles through theunique methods of exfoliation as described above. Some of these polymerdispersions and solutions may include but are not limited to plastisols,caulks, sealants, paints, and coatings.

EXAMPLES

The following materials were used for the examples:

a. Microthene™ FE532 EVA [24937-78-8], 8 to 9% vinyl acetate, meltindex=9.5, from Equistar

b. Microthene™ FN519 LDPE [9002-88-4] from Equistar

c. Microthene™ FP800 PP [9003-07-0] from Equistar

d. Microthene™ FN510 LDPE [9002-88-4] from Equistar

e. Microthene™ FN501 LDPE [9002-88-4] from Equistar

f. Microthene™ FA700 HDPE [25087-34-7] from Equistar

g. Epolene E43P maleated polypropylene from Eastman

h. Epolene C16P maleated polyethylene from Eastman

i. Diisononylphthalate (DINP)

j. Dioctylphthalate (DOP)

k. Dibutylphthalate (DBP)

l. Mineral Oil, white heavy [8020-83-5] Aldrich; and both Drakeol 10 &35 from Penrico

m. Corfree M1 [72162-23-3] mixture of undecanedioic acid (C8),dodecanedioic acid (C9), and sebacic acid (C10); from duPont

n. 1,12-dodecanedicarboxylic acid [821-38-5]

o. Sebacic acid [111-20-6]

p. Stearic acid

q. Irganox 1010 antioxidant from Ciba

r. Irganox PS800 [123-28-4] from Ciba

s. Nicron 302, magnesium silicate powder (talc), 13 micron particle size

t. National Starch hot melt adhesive

u. EQM-PE; maleated polyethylene from Equistar

v. Permalyn 3100; rosin ester of pentaerythritol (Eastman)

w. Piccotac B; mixed hydrocarbon tackifier (Eastman)

x. EQ-EVA; poly(ethylene-co-vinyl acetate), 18% vinyl acetate fromEquistar

y. Isostearic Acid [2724-58-5], Emersol 875 from Henkel

z. Omya, 30 micron, calcium carbonate powder

aa. Capa 6501, polycaprolactone from Solvay

bb. Nanomer I-44, surface treated nano-sized montmorillonite (Nanocor)

cc. Elvax 4355, polyethylene-co-vinyl acetate-co-methacrylic acid, 25%VA, 0.7-1.4% MA, M.I.=6 (duPont)

dd. Nucrel 3990, polyethylene-co-methacrylic acid, 9% MA, M.I.=10(duPont)ee. Acrawax C, N,N′-ethylenebisstearamide [110-30-5], Lonza Group

ff. EVA-1, Poly(ethylene-co-vinyl acetate), 9% VA, melt index=3.0, fromEquistar

gg. EVA-2, Poly(ethylene-co-vinyl acetate), 12% VA, melt index=3.0, fromEquistar

hh. EVA-3, Poly(ethylene-co-vinyl acetate), 15% VA, melt index=3.0, fromEquistar

ii. PSMA, poly(styrene-co-maleic acid), [65652-36-0], Aldrich catalog#43,527-9

jj. Celogen 754-A, azodicarbonamide with ZnO catalyst [123-77-3],Crompton Corporation

kk. E-C 597A Maleated polypropylene, Honeywell Corporation

ll. A-CX Grade 2440 polypropylene wax, A-C Performance Products, adivision of Honeywell Corporation

Unless otherwise specified, a common experimental procedure was used forpreparing adhesives, for hot melting/mixing, for application of theadhesive to a polymer/clay coated paper substrate, and for adhesiontesting. The “liquid form” of the adhesives was prepared by dispersingthe solid ingredients into the liquids at room temperature (into 40 mlglass jars with lids). The dispersions were hand mixed with a spatula.An aliquot of the adhesive (1 to 2 grams) was placed onto a 4″×4″ pieceof aluminum foil. The foil was placed onto a hot plate at a specifiedtemperature, and was allowed to set for one minute. The “hot melt” formof the adhesives were then mixed with a spatula until visual homogeneitywas achieved. At this point, one half of a 2 cm×3 cm polymer/clay coatedpaper coupon (common stock from either a cereal box or beverage package)was dipped into the hot melt solution so that the coated side of thepaper (the printed side) was half-covered with the hot melt solution.The coupon was removed and was immediately pressed (with moderatepressure by hand) against one-half of a second coupon of equal size sothat the hot melt was sandwiched between the coated paper coupons inlap-shear fashion. Moderate pressure was maintained for 10 seconds, andthen the sample was allowed to cool. After cooling to room temperature,and after a specified period of time, the lap shear samples were twistedby hand to force a tearing failure at the bonded interface. Cohesivefailure in the paper stock was deemed as a “pass,” and any other type offailure was deemed as “fail.”

Example 1

This example illustrates the relative adhesion performance andcompatibility of several solid/liquid dispersions (Table 1).

TABLE 1 Example 1 Formulations Sam- Compo- Compo- ple Component A nent BComponent C nent D 1-1   5 g FA700 HDPE None 3.5 g DINP None 1-2   5 gFP800 PP None 3.9 g DINP None 1-3   5 g FE532 EVA None   4 g DINP None1-4   5 g E43P maleated PP None   5 g mineral oil None 1-5   5 g FN-519LDPE None   3 g DINP None 1-6   5 g F532 EVA None   4 g mineral oil None1-7   4 g FP800 PP None 3.2 g mineral oil None 1-8 1.5 g stearic acidNone 4.2 g mineral oil None 1-9   4 g FP800 PP None 3.2 g mineral oilNone 1-10   5 g FE532 EVA None   4 g DBP None 1-11   5 g E43P maleatedPP None   5 g DINP None 1-12   5 g FP800 PP None None None 1-13   5 gC16P maleated PE None 3.6 g mineral oil None 1-14   5 g C16P maleated PENone None None 1-15   5 g FA700 HDPE None 3.5 g DOP None 1-16   5 gPermalyn 3100 None   5 g mineral oil None 1-17   5 g Piccotac B None   5g mineral oil None 1-18   5 g E43P maleated PP None   5 g Isostearicacid None 1-19   5 g FE532 WVA None   5 g Isostearic acid None 1-20   5g Acrawax C None   5 g mineral oil None 1-21   5 g PSMA None   5 g DBPNone 1-22   5 g PSMA None   5 g mineral oil None

The solid/liquid ratio was chosen in each case to insure that thedispersions behaved as liquids at room temperature. The liquiddispersions in Table 1 fused to become molten liquids at elevatedtemperatures. All samples except for 1-16 and 1-17 gelled to becomesolid blends upon cooling.

After hot melt mixing at 385° F., adhesion coupons were prepared (asdescribed above), and the remainder of each sample was allowed to coolto room temperature on aluminum foil. The samples were visuallyinspected for compatibility while mixing, for exudation upon cooling,and for exudation after 24 hours. After cooling, the relative propertieswere qualitatively evaluated, and paper adhesion was tested as describedabove. The results are given in Table 2.

TABLE 2 Results of Example 1 Experiments Exudation ExudationCompatibility Upon Qualitative Polymer After 24 Sample Upon MixingCooling Properties Hours Adhesion 1-1 Liquid phase None Opaque, toughSlight Fail separation 1-2 Compatible None Opaque, weak, waxy None Fail1-3 Compatible Slight Opaque, tough, Severe Fail elastomeric 1-4Compatible None Opaque, weak, waxy None Fail 1-5 Compatible SlightOpaque, tough Severe Fail 1-6 Compatible Slight Opaque, tough, SevereFail elastomeric 1-7 Compatible None Opaque, weak, waxy None Fail 1-8Compatible None Wax None Fail 1-9 Compatible None Opaque, weak, waxyNone Fail 1-10 Compatible Slight Opaque, tough, Severe Fail elastomeric1-11 Compatible None Opaque, weak, waxy None Fail 1-12 N/A N/A Opaque,tough N/A Fail 1-13 Compatible Slight Waxy, weak Severe Fail 1-14 N/AN/A Opaque, tough N/A Pass 1-15 Liquid phase None Opaque, tough NoneFail separation 1-16 Compatible None Liquid solution None Fail 1-17Compatible None Liquid solution None Fail 1-18 Compatible None Opaque,weak, waxy None Fail 1-19 Compatible Slight Opaque, tough, Severe Failelastomeric 1-20 Compatible None Opaque, weak, waxy None Fail 1-21Compatible None Semi-rigid, brittle None Fail 1-22 Incompatible ExtremeBrittle Extreme Fail

It is surprising to note that out of all the polyolefins tested, onlythe polypropylene homopolymer and the maleated polypropylene copolymerwere capable of forming non-exuding solid blends with liquids likemineral oil, isostearic acid, and DINP. Although the solid HDPE/DOPblend is non-exuding, the blend is incompatible when the HDPE is in themolten state. Based on inspection of solubility parameters, it isimportant to note that these results would not be anticipated by thoseskilled in the art of making polymer/liquid blends. For example, thesolubility parameters in MPa^(1/2) for PE, EVA, and PP rangerespectively from 15.76 to 17.99 for PE; 17.0 to 18.6 for EVA; and 18.8to 19.2 for PP. On the other hand, the solubility parameters forparaffinic hydrocarbons (such as those that comprise mineral oil) rangefrom 15 to 18 (see Polymer Handbook, J. Brandrup and E. H. Immergut,Editors, John Wiley and Sons, New York, pp. VII-552-553). Thus, based onthe similar differences in solubility parameters between the mineral oiland each polyolefin, there is no reason to suspect that one combinationwould be more or less compatible than another.

It is also surprising that the PP/DINP blends are free from exudation,whereas EVA/DINP blends are not; especially given that DINP is morepolar than mineral oil, and EVA is more polar than PP. It is also ofinterest that the finished HDPE/DOP blends are compatible, whereas thehigher molecular weight DINP shows signs of exudation. Furthermore,unlike the other polyolefins, HDPE appears to be less compatible withthe liquid in the molten state. Placing the molten HDPE/DOP andHDPE/DINP blends directly onto adsorbent paper towels served to furtherverify this visual observation. The paper became immediately saturatedwith the liquid. Similar tests were also performed with maleatedPP/mineral oil blends, but no visual evidence of saturation wasobserved.

The results in Table 2 also show that with the exception of HDPE/DOPblends, liquid adsorption is accompanied by a qualitative decrease instrength as can be seen by comparing neat PP (1-12) with the liquid/PPblends. Furthermore, although the other polyolefin/liquid blends tend toretain higher levels of toughness and strength, their exudation isextreme. Hence, none of the polymer/liquid blends in this example hasthe requisite cohesive strength and/or liquid compatibility to produceacceptable adhesion to paper (as judged by the poor adhesion results).Only the neat maleated PE displays adequate adhesion to paper; but whenblended with mineral oil, its adhesion decreases, its strengthdeteriorates, and its liquid component (mineral oil) exudes.

It is also noteworthy that stearic acid, like PP and maleated PP, iscapable of adsorbing liquids like mineral oil. However, the resultantlow molecular weight gel has even less cohesive strength than thecompatible PP/liquid blends, and thus it cannot be used as an adhesiveby itself. Acrawax C and PSMA are also capable of adsorbing mineral oiland DBP, respectively, but no adhesion is achieved. Further, the solidtackifiers, Piccotac B and Permalyn 3100, fuse with mineral oil toproduce compatible, liquid solutions at room temperature. Needless tosay, these liquids have no cohesive strength.

Example 2

This example demonstrates the feasibility of using multiple componentliquid dispersions to both minimize exudation and to maintain sufficientcohesive strength in the finished adhesive. The candidates for“Component B” in these formulations are chosen based on their ability toprevent liquid exudation by themselves as shown in Example 1. Note thatthe “diacid” in this example refers to dodecanedioic acid. Theformulations are provided in Table 3.

TABLE 3 Example 2 Formulations; Multicomponent Blends Sample Component AComponent B Component C Component D 2-1 5 g FE532 EVA None 4.2 g mineraloil None 2-2 5 g F532 EVA 2 g stearic acid 4.2 g mineral oil None 2-3 5g FE532 EVA 1.5 g stearic acid 4.2 g mineral oil 0.7 g diacid 2-4 5 gFA700 HDPE None 4.2 g mineral oil None 2-5 5 g FA700 HDPE 2 g stearicacid 4.2 g mineral oil None 2-6 5 g FA700 HDPE None 4.2 g mineral oil 2g diacid 2-7 5 g FA700 HDPE 1.5 g stearic acid 4.2 g mineral oil 0.7 gdiacid 2-8 5 g FN-519 None 4.2 g mineral oil None LDPE 2-9 5 g FN-519 2g stearic acid 4.2 g mineral oil None LDPE 2-10 5 g FN-519 None 4.2 gmineral oil 2 g diacid LDPE 2-11 5 g FN-519 1.5 g stearic acid 4.2 gmineral oil 0.7 g diacid LDPE 2-12 5 g F532 EVA 1.5 g FP800 PP 4.2 gmineral oil 0.7 g diacid 2-13 5 g F532 EVA 1.5 g E43P 3.8 g mineral oil0.7 g diacid 2-14 3.5 g F532 EVA 3 g E43P 3.9 g mineral oil 0.7 g diacid2-15 3.5 g F532 EVA 3 g E43P 3.9 g DINP 0.7 g diacid 2-16 3.5 g FP800 PP3 g E43P 3.9 g mineral oil 0.7 g diacid 2-17 3.5 g C16P 3 g FA700 HDPE 4g DOP None 2-18 3.5 g C16P 3 g FA700 HDPE 4 g DOP 0.7 g diacid 2-19 3.5g C16P 3 g E43P 3.9 g mineral oil 0.7 g diacid 2-20 3.5 g F532 EVA 3 gFA700 HDPE 4 g DOP 0.7 g diacid 2-21 3.5 g F532 EVA 1.5 g E43P/1.5 gFA700 2 g DOP/2 g mineral 0.7 g diacid HDPE oil 2-22 3.5 g EQM PE 3 gE43P 4 g mineral oil 0.7 g diacid 2-23 46 EQM PE 2.5 g E43P 4.5 gmineral oil 0.7 g diacid 2-24 4 g F532 EVA 2.5 g E43P 4.5 g mineral oil0.7 g diacid 2-25 2.6 g F532 EVA 4 g E43P 3.5 g mineral oil 0.7 g diacid2-26 4.5 g F532 EVA 2.0 g E43P 5 g mineral oil 0.7 g sebacic acid 2-274.5 g F532 EVA 2.0 g Permalyn 3100 5 g mineral oil 0.7 g sebacic acid2-28 4.5 g F532 EVA 1.5 g E43P/0.5 g Permalyn 5 g mineral oil 0.7 gsebacic 3100 acid 2-29 4.5 g F532 EVA 1.5 g E43P/0.5 g Permalyn 5 gmineral oil 0.7 g sebacic 3100 acid 2-30 4.0 g F532 EVA 2.5 g E43P 5 gmineral oil 0.7 g diacid 2-31 4.5 g F532 EVA 2.0 g E43P 5 g isostearicacid 0.7 g sebacic acid 2-32 4.5 g EQM PE 2.0 g E43P 5 g mineral oil 0.7g diacid 2-33 4.5 g EQM PE 2.0 g E43P 5 g isostearic acid 0.7 g diacid2-34 4.5 g F532 EVA 2.0 g Acrawax C 5 g mineral oil 0.7 g sebacic acid2-35 5 g F532 EVA 2.4 g PSMA 5 g DBP 0.7 g sebacic acid

After hot melt mixing at 385° F., adhesion coupons were prepared, andthe remainder of each sample was allowed to cool to room temperature onaluminum foil. The samples were visually inspected for exudation uponcooling, and for exudation after 24 hours. Paper adhesion was tested asdescribed above. The results are given in Table 4.

TABLE 4 Performance of Example 2 Formulations Exudation ExudationAdhesion Number of Sample Upon Cooling After 24 Hours Passes Out of 52-1 High High 0 2-2 None Slight 0 2-3 None None 5 2-4 High High 0 2-5None None 0 2-6 None Slight 0 2-7 None None 0 2-8 High High 0 2-9 NoneNone 0 2-10 None Slight 0 2-11 None None 0 2-12 None None 0 2-13 NoneNone 5 2-14 None None 5 2-15 None None 1 2-16 None None 0 2-17 None None0 2-18 None None 0 2-19 None None 1 2-20 None None 0 2-21 None None 52-22 None None 5 2-23 None None 3 2-24 None None 5 2-25 None None 0 2-26None None 5 2-27 None None 0 2-28 None None 5 2-29 None None 5 2-30 NoneNone 5 2-31 None None 0 2-32 None Slight 5 2-33 None None 0 2-34 NoneNone 0 2-35 None None 0

Samples 2-1 to 2-3 show that when stearic acid is blended with EVA,exudation is greatly decreased, but no adhesion is observed.Surprisingly, when a second acid is added (dodecanedioic acid),exudation is further reduced, and adhesion to paper stock is excellent.Samples 2-4 to 2-11 also show that stearic acid prevents exudation ofmineral oil from both HDPE and LDPE. Dodecanedioic acid also providessome benefit. However, only the EVA/stearic acid/dodecanedioic acidblend provides adhesion. Thus, the prevention of exudation alone is notenough to insure adhesion. Instead, at least one of the components musthave functionality that is capable of bonding with the substrate, eitheralone or through activation with another additive.

Samples 2-12 to 2-15 make use of polypropylene and maleatedpolypropylene as alternatives to stearic acid. Like stearic acid, thesepolymers also prevent exudation of liquids from EVA. Surprisinglyhowever, only maleated polypropylene with mineral oil provides adequateadhesion. Even though exudation is minimal, adhesion does not occur withpolypropylene homopolymer (even in the presence of dodecanedioic acid).Also, only partial adhesion is achieved with DINP in place of mineraloil. These results further illustrate that minimizing exudation is initself not enough to enable adhesion. Instead, the combination of lowexudation, polymer functionality, liquid type, and secondary additivesare all critical.

Sample 2-20 makes use of HDPE and DOP in place of maleated polypropyleneand mineral oil. Based on the results from Example 1, HDPE prevents theexudation of DOP like both stearic acid, and like maleated PP withmineral oil. Interestingly, when HDPE and DOP are blended with EVA,exudation is prevented, but no adhesion occurs. Surprisingly however,when HDPE/DOP and maleated polypropylene/mineral oil are used incombination (sample 20-21), adhesion does occur. Again, this resultshows that multicomponent blends can be used in unexpected ways to bothprevent exudation, and to improve adhesion.

Samples 2-16 to 2-19 make use of the “adsorbent” polymer/liquidcombinations that were discussed in Example 1, but with alternatives toEVA as the primary polymer component. Sample 2-16 makes use ofpolypropylene blended with maleated polypropylene and mineral oil.Unlike EVA, polypropylene is capable of adsorbing mineral oil (seeExample 1). However, the resultant finished adhesive is cohesively weakand waxy, and no adhesion is observed. Thus, it is important that theblend contain a primary polymer component (the “reinforcing phase” asdefined in this invention), which by itself, is incompatible with theliquid. In this way, the primary component can provide the adhesive withstrength, and the secondary component (i.e., the “adsorbent phase”) canadsorb the liquid to prevent exudation. Further illustration of thiscomes from sample 2-25, which contains an excess of maleatedpolypropylene as the adsorbent polymer blended with EVA. This blend doesnot exude, but unlike its sample 2-14 counterpart (with EVA in excess),no adhesion is observed. Instead, this blend is cohesively weak and waxylike sample 2-16.

Sample 2-17 makes use of maleated polyethylene blended with an HDPEadsorbent phase, and DOP. This adhesive qualitatively has moderatecohesive strength, and it exhibits no exudation. However, it alsoexhibits no adhesion to paper, much like its sample 2-20 counterpart(with EVA instead of maleated polyethylene). Even the addition ofdodecanedioic acid (sample 2-18) does not improve adhesion. Again, theseresults further illustrate that minimizing exudation is in itself notenough to enable adhesion. Instead, the combination of low exudation,polymer functionality, liquid type, and secondary additives may all beimportant.

When C16P maleated polyethylene is used in place of EVA in blends withmaleated polypropylene and mineral oil, exudation is minimal, and thereis some evidence of adhesion (sample 2-19). However, the adhesive iscohesively weaker than its EVA/maleated polypropylene/mineral oilcounterpart (sample 2-14). On the other hand, when the C16P issubstituted with a qualitatively higher melt viscosity and thereforehigher molecular weight maleated polyethylene (sample 2-22 and sample2-32), the resultant paper adhesion is as good as sample 2-14 (withEVA). Thus, it is also important that the reinforcing polymer (thepolymer which by itself is incompatible with the liquid) be ofsufficient molecular weight to impart cohesive strength to the adhesive.

As stated earlier, the reinforcing polymer must also be present at anadequate level in the overall formulation. For example, samples 2-23with EQ maleated PE, and 2-24 with EVA, both make use of higher mineraloil levels (a desirable condition for reducing the viscosities of thedispersion and the melt). At higher mineral oil levels, more reinforcingpolymer is also required to maintain cohesive strength (as will be shownin a subsequent example). When employed at the same levels, only the EVAhas sufficient strength to provide adequate adhesion. Thus, althoughother reinforcing polymers can be used (such as maleated PE), thepreferred ratios of ingredients will vary depending upon the nature ofthe reinforcing polymer.

Acids other than dodecanedioic acid can also be used to produce adequateadhesion as shown by sample 2-26, which makes use of sebacic acidtogether with maleated polypropylene as the adsorbent phase. Tackifierscan also be employed to reduce the melt viscosity of the formulation,and to help prevent exudation of the liquid phase. However, whenPermalyn 3100 (a pentaerythritol rosin ester “tackifier”) is substitutedfor maleated polypropylene in sample 2-27, no adhesion is observed.Given that Permalyn-3100 is compatible with mineral oil (as shown inExample 1), it is reasonable to assume that it may be a good adsorbentphase candidate for use in blended formulations. As suspected, Permalyn3100 prevents exudation, but the resultant blend with EVA issurprisingly weak and waxy (unlike formulations made with either stearicacid or maleated PP). Thus, as shown in the preceding examples,compatibility with the liquid carrier alone is not a sufficientcondition for choosing a good adsorbent phase material. Surprisingly,however, a small amount of Permalyn 3100 can be incorporated into theformulation if blended with maleated polypropylene as the adsorbentphase (Sample 2-28). Similarly, Piccotac B, a traditional hydrocarbontackifier for hot melt adhesives, can also be incorporated as acomponent of the adsorbent phase when blended with maleated PP (sample2-29).

Tackifier additives are often used in traditional hot melt adhesiveapplications to achieve lower melt viscosities, and to improve adhesionto certain substrates. For the purposes of this invention, tackifierslike Permalyn 3100 and Piccotac B can be incorporated, but only insofaras the cohesive strength of the resultant adhesive is not undulycompromised.

Samples 2-31 and 2-33 make use of isostearic acid as an alternativeliquid phase to mineral oil. As shown in Example 1, isostearic acid iscompatible with maleated PP after melt blending. This effect is alsomanifested in the multi-component blends of this example, where bothadhesives exhibit qualitatively moderate cohesive strengths withoutsigns of exudation. Surprisingly however, the adhesives with isostearicacid as the liquid phase do not adhere to paper, unlike their 2-26 and2-32 mineral oil counterparts (with EVA and maleated polyethylene as thereinforcing phases, respectively). Samples 2-34 and 2-35 are alsonon-exuding as might be anticipated from the results presented inExample 1. Surprisingly however, these samples do not adhere to paper.Again, these results further illustrate that minimizing exudation is initself not enough to enable adhesion.

Example 3

This example demonstrates the surprising effect that the adsorbent phasecan have on the moderate temperature storage stability of the liquiddispersions. As shown in Example 2, certain adsorbent phase candidatesare capable of producing finished adhesives that exhibit minimalexudation, and excellent adhesion to paper. However, many of theseadsorbent phase candidates tend to negatively impact the storagestability of the liquid dispersions. Surprisingly, however, it has beenfound that certain adsorbent phase materials do not negatively affectthe storage stability; and as such, they define a preferred embodimentof this invention.

The formulations for this example (given in Table 5) were chosen fromthose that provided both adequate adhesion and minimal exudation asillustrated in Example 2. In addition, several of the ingredients wereseparately dispersed into mineral oil for testing. The dispersions wereplaced into a gravity oven set at 122° F. (50° C.) for a period of 24hours. The samples were then removed and allowed to cool to roomtemperature. Using a spatula, the viscosities were qualitativelycompared to the viscosities of samples that were retained at roomtemperature. The change in viscosity was qualitatively reported aseither “no change,” “slight increase,” or “gelation.” Results arereported in Table 6.

TABLE 5 Liquid Dispersions Tested For Shelf Stability at 122° F. SampleComponent A Component B Component C Component D 2-1 5 g FE532 EVA None4.2 g mineral oil None 2-2 5 g F532 EVA 2 g stearic acid 4.2 g mineraloil None 2-3 5 g FE532 EVA 1.5 g stearic acid 4.2 g mineral oil 0.7 gdiacid 1-8 1.5 g stearic None 4.2 g mineral oil None acid 3-1 None None4.2 g mineral oil 0.7 g diacid 3-2 None 2.5 g E43P 5 g mineral oil None1-4 5 g E43P None 5 g mineral oil None 2-30 4.0 g F532 EVA 2.5 g E43P 5g mineral oil 0.7 g diacid 2-21 3.5 g F532 EVA 1.5 g E43P/1.5 g 2 gDOP/2 g mineral oil 0.7 g diacid FA700 HDPE 3-3 None 5 g FA700 HDPE 3.5g DOP None 3-4 5 g EQ-EVA None 4.2 g mineral oil None

TABLE 6 Qualitative Viscosity Change After Exposure to 122° F. SampleQualitative Viscosity Change 2-1 Slight increase 2-2 Gelation 2-3Gelation 1-8 Gelation 3-1 No change 3-2 No change 1-4 Slight increase2-30 No change 2-21 Gelation 3-3 Gelation 3-4 Gelation

The results of Table 6 demonstrate that certain adsorbent phasematerials will actually adsorb the liquid phase at moderatetemperatures. Liquid dispersions containing such ingredients can stillform useful and novel adhesives, but if moderate temperature storagestability is desirable, then the adsorbent phase must remain disperseduntil the material is exposed to higher temperatures (as would be doneduring the processing of the adhesive). The results show that stearicacid leads to low temperature gelation, as does HDPE with DOP. Thedicarboxylic acid does not cause gelation, nor does EVA, unless itsvinyl acetate content is increased (sample 3-4). The higher vinylacetate content equates to a lower Tg, less crystallinity, and betteradsorption of mineral oil. Thus, when mineral oil is chosen as theliquid carrier, the ethylene copolymer should be chosen so as tominimize its solubility and adsorption so that adequate storagestability can be achieved.

Surprisingly, when formulation 2-30 is exposed to 122° F., its viscosityremains stable, as does maleated PP when it is dispersed alone inmineral oil (3-2). Thus, when exposed to moderate temperatures, themaleated PP does not adsorb significant levels of mineral oil, at leastat the concentrations employed in formulation 2-30. In spite of this,and of equal surprise, the maleated PP is able to retain mineral oilwhen it is melt blended and cooled as shown in Example 1. Also,formulations containing maleated PP exhibit good adhesion and minimalexudation as shown in Example 2 (like sample 2-30).

Although not wishing to be bound by any single theory, it appears that agood adsorbent phase for this application is a crystalline orsemicrystalline material that does not adsorb the liquid phase until itis molten. Further, the melt point of the adsorbent phase should behigher than the highest anticipated storage temperature for the liquiddispersion. Unlike maleated PP, stearic acid dissolves and melts in themineral oil at moderate temperatures. Upon cooling, the stearic acidthen phase separates, recrystallizes, and gels with the mineral oil.Although this effect is desirable for achieving adequate adhesion andminimal exudation, if the effect occurs prematurely during end-usestorage, the liquid dispersion will prematurely gel.

Upon recrystallization, the adsorbent phase material must also be ableto retain the liquid phase. This is indeed the case for both stearicacid and maleated PP with mineral oil, and for HDPE with DOP. However,of the three examples cited here, only the maleated PP displays theunique capability of providing adequate end-use adhesion, and acceptablestorage stability.

Example 4

This example demonstrates the effect of mixing (and hence the effect ofthe application process) on the resultant adhesion. Sample 2-30 washeated on a hot plate at 385° F., and was mixed according to theprocedure outlined above. A second sample of the same formulation washeated, but without mixing. Adhesion coupons were prepared in both casesfor relative comparison. The mixed sample exhibited fiber tear adhesion5 out of 5 times, whereas the unmixed sample provided no adhesion. Inthe absence of mixing, the cohesive strength of the adhesive wassignificantly reduced. Thus, this example demonstrates a preferredmethod for applying the adhesive of this invention. The adhesive musteither be premixed, or it must be mixed during the application process,otherwise the adhesive will not produce adequate adhesion to thesubstrate.

Example 5

This example demonstrates the effect of temperature on adhesion in thepresence and absence of diacid. It also demonstrates the effect of mixeddicarboxylic acid additives on adhesion. The procedures are the same asthose used in Example 2, except samples were processed at temperaturesof 345° F., 385° F., and 430° F. Table 7 provides the comparativeformulations for this example, and Table 8 provides the results,including exudation upon cooling, exudation after 24 hours, and adhesionto paper. The exudation results were judged for samples that wereprocessed at 385° F., whereas adhesion was judged at all threetemperatures.

TABLE 7 Formulations for Example 5 Sample Component A Component BComponent C Component D 5-1 3.5 g FE532 EVA   3 g E43P 4.0 g mineral oilNone 5-2 3.5 g FE532 EVA   3 g E43P 4.0 g mineral oil 0.7 gdodecanedioic acid (diacid) 5-3 4.0 g FE532 EVA 2.5 g E43P 4.5 g mineraloil None 5-4 4.0 g FE532 EVA 2.5 g E43P 4.5 g mineral oil 0.7 g diacid5-5 4.0 g FE532 EVA 2.5 g E43P 4.5 g mineral oil 1.0 g diacid 5-6 4.0 gFE532 EVA 2.5 g E43P 4.5 g mineral oil 1.5 g diacid 5-7 4.0 g FE532 EVA2.5 g E43P 4.5 g mineral oil 0.7 g sebacic acid 5-8 4.0 g FE532 EVA 2.5g E43P   5 g mineral oil 0.7 g diacid 5-9 3.5 g FE532 EVA   3 g E43P 4.0g mineral oil 0.7 g Corfree M1

TABLE 8 Performance of Example 2 Formulations Adhesion Number of PassesOut of 5, Exudation Exudation Processed at Sample Upon Cooling After 24Hours 345° F./385° F./430° F. 5-1 None Slight 0/0/2 5-2 None None 5/5/55-3 None Slight 0/0/1 5-4 None None 5/5/5 5-5 None None 5/5/5 5-6 NoneNone 5/5/5 5-7 None None 5/5/not tested 5-8 None None 5/5/not tested 5-9None Slight 0/1/0

These results show that in the absence of a dicarboxylic acid, exudationoccurs, and the resultant adhesion is poor. Also, the addition of adicarboxylic acid such as dodecanedioic acid or sebacic acid producesacceptable adhesion at significantly reduced process temperatures.Interestingly, the level of the diacid has little effect on theresultant adhesion (at least when used at levels above 0.7 g in theseformulations). Thus, the composition should contain preferably betweenzero and 15% of a dicarboxylic acid “activator” by weight. Surprisingly,a mixture of dicarboxylic acids (e.g. Corfree M1, which containsfractions of both dodecanedioic acid and sebacic acid) does not improveadhesion.

Thus, the preferred adhesive of this invention is comprised of adicarboxylic acid “activator” additive such as dodecanedioic acid orsebacic acid. These additives not only minimize exudation as shown hereand in Example 2, but they also lower the minimum threshold temperaturerequired to achieve adhesion. Hence, the preferred method of applicationnot only involves mixing as shown in Example 4, it involves heating theadhesive to a certain minimum threshold temperature so as to achieveadhesion, where the minimum threshold temperature is affected by thepresence or absence of a dicarboxylic acid in the formulation.

Example 6

This example describes the effect of component ratios on viscosity,shelf stability, and adhesion. The formulations listed in Table 9 weremade according to procedures outlined in Examples 1 and 2. The level ofsebacic acid was kept constant (at 0.7 g) as was the total level ofresin (at 6.5 g), while the ratio of adsorbent phase to reinforcingphase was varied, as was the level of liquid. After hot melt mixing at385° F., adhesion coupons were prepared, and the remainder of eachsample was allowed to cool to room temperature on aluminum foil. Thesamples were visually inspected for exudation after 24 hours, and after20 days. The samples were qualitatively compared and ranked via arelative numeric scale (1=lowest, 4=highest).

Paper adhesion was tested (as described in Example 2) after 1 day andafter 20 days (number of passes out of 5 coupons). Each adhesive (inliquid dispersion form) was also placed in a 65° C. oven for 24 hours totest shelf stability as judged by the relative increase in viscosity.The viscosities were qualitatively compared and ranked via a relativenumeric scale (1=lowest, 7=highest). The results are given in Table 10.

TABLE 9 Formulations Tested in Example 6 FE532 EVA Maleated PP MineralOil Sample (reinforcing phase) (adsorbent phase) (liquid phase) 6-1 4.0g 2.5 g 5.0 g 6-2 4.0 g 2.5 g 5.5 g 6-3 4.0 g 2.5 g 6.0 g 6-4 4.25 g 2.25 g  5.0 g 6-5 4.25 g  2.25 g  5.5 g 6-6 4.25 g  2.25 g  6.0 g 6-74.5 g 2.0 g 5.0 g 6-8 4.5 g 2.0 g 5.5 g 6-9 4.5 g 2.0 g 6.0 g

TABLE 10 Relative Ranking of Exudation, Adhesion and Liquid DispersionViscosity Exudation Exudation Adhesion Adhesion @ 1 @ 20 @ 1 @ 20 SampleDay Days Day Days Viscosity 6-1 None 1 5 5 5 6-2 None 1 4 5 3 6-3 None 25 5 1 6-4 None 2 5 5 6 6-5 None 3 5 5 4 6-6 None 3 5 5 2 6-7 None 4 5 47 6-8 None 3 3 4 5 6-9 None 4 3 4 4

Although none of the samples exhibits immediate exudation, the level ofexudation generally increases as the level of the adsorbent phase isdecreased, and as the level of liquid phase is increased. Similarly, thesamples with the best adhesion are those that have higher ratios of theadsorbent phase to the liquid phase (i.e. those that exhibit the lowestlevels of exudation).

The viscosities of the dispersions (after exposure to 65° C.) decreasewith increasing levels of liquid phase, but they surprisingly decreasewith increasing levels of the adsorbent phase. This result is parallelto that reported in Example 3. Even when exposed to elevatedtemperatures, dispersions with maleated polypropylene adsorb the leastamount of mineral oil. In spite of this, and of equal surprise,formulations with the highest levels of maleated PP are able to retainmineral oil when they are melt-blended and cooled. Also, formulationscontaining maleated PP exhibit good adhesion and minimal exudation.

Example 7

This example demonstrates the use of heat stabilizers and inorganicadditives in the adhesive formulations of this invention. Theformulations (shown in Table 11) were made according to proceduresoutlined in Examples 1 and 2. After hot melt mixing at 385° F., adhesioncoupons were prepared, and the remainder of each sample was allowed tocool to room temperature on aluminum foil. The samples were visuallyinspected for exudation after 24 hours. Paper adhesion was tested (asdescribed in Example 2) after 1 day. Each adhesive (in liquid dispersionform) was also placed in a 45° C. oven for 24 hours to test shelfstability as judged by the relative increase in viscosity. The resultsreported in Table 12 show that the formulations exhibit good adhesion,minimal exudation, and good shelf stability at moderate temperatures.

TABLE 11 Formulations Used in Example 7 7-1 (weight % of 7-2 (weight %of 7-1 (weight % of Material each component) each component) eachcomponent) FE 532 EVA 29.43 26.01 26.01 Maleated PP 18.39 11.56 8.09Mineral Oil 36.79 34.68 34.68 Stearic acid 0.24 0 0 Sebacic acid 5.154.05 4.05 Nicron 302 talc 10.0 0 0 Omya calcium 0 23.12 23.12 carbonateIrganox 1010 0 0.29 0.29 Irganox PS800 0 0.29 0.29 Permalyn 3100 0 03.47

TABLE 12 Results of Adhesion, Exudation, and Shelf Stability Evaluationsof Example 7 Formulations Exudation at 24 Viscosity change Sample hoursAdhesion (#pass/5) after 45° C. exposure 7-1 None 5 No change 7-2 None 5No change 7-3 None 5 No change

Example 8

This example demonstrates the effect of the liquid adsorbent phase onthe “set time” of the adhesive. The “set time” in this example isdefined as the time required for the adhesive to change from a moltenliquid to a solid. In all cases, 1.0 g of each formulation wasmelt-blended at 385° F. according to procedures in Examples 1 and 2. Thesamples were removed from the hot plate and placed on a bench top atroom temperature to cool. The adhesives were visually monitored for the“onset time of set,” or the time required for the first sign ofcrystallization to appear as visually monitored by the appearance of anysign of opacity. The “set time” of the adhesives was recorded as thetime required for the entire adhesive to appear opaque. At this point,the adhesive was also observed to be solid as judged by pressing it witha metal spatula. Formulations for this example are provided in Table 13,and results are presented in Table 14.

TABLE 13 Formulations Used in Example 8 Commercial Dodecane- Hot MeltSam- FE532 Maleated Stearic dioic Mineral (National ple EVA PP Acid acidoil Starch) 8-1 0 0 0 0 0 100% 8-2 5 g 0 1.5 g 0.7 g 4.2 g 0 8-3 4 g 2.5g 0 0 4.5 g 0 8-4 4 g 2.5 g 0 0.7 g 4.5 g 0 8-5 4 g 2.5 g 0 1.0 g 4.5 g0 8-6 4 g 2.5 g 0 1.5 g 4.5 g 0 8-7 3.5 g   3 g 0 1.0 g 4.0 g 0

TABLE 14 Effect of Formulations on the Relative “Onset Time of Set” andon the “Set Time” Sample Onset Time of Set (seconds) Set Time (seconds)8-1 15 55 8-2 14 45 8-3 10 35 8-4 10 35 8-5 10 40 8-6 5 40 8-7 5 35

In spite of being formulated with low molecular weight mineral oil, eventhe sample with stearic acid as the adsorbent phase exhibits faster setthan the comparative commercial adhesive. The set time is observed toslightly decrease as the dodecanedioic acid level is increased, but thedecrease in set time is most dramatic as the ratio of maleated PP tomineral oil is increased. This example shows that the set time of theformulations of this invention can be controlled by varying thecompositions, and that set times can be achieved which are on par withthose of traditional hot melt adhesives.

Example 9

This example demonstrates the effect of the reinforcing phase copolymercomposition on adhesive performance. In example 3, an ethylene copolymerwith a higher level of vinyl acetate of 18% VA (sample 3-4) was shown tohave worse shelf stability than a copolymer with 9% VA when the polymerparticles were dispersed in mineral oil. However, a higher vinyl acetatelevel, particularly when copolymerized with an additional monomer suchas methacrylic acid, or maleic anhydride, can yield a particularlyuseful polymer for the purposes of this invention. Because of thedetrimental effect on shelf stability, polymer particles of this typeshould be protected with a coating layer of a polymer that is notpermeated by the liquid phase until the temperature is raised beyondsome critical level. In this way, the core of the particle would not bepermeated prematurely by liquid, and the dispersion would be shelfstable. Such a coating could be for example, an ethylene copolymer witha lower vinyl acetate content, a copolymer of ethylene and methacrylicacid, a polysiloxane, polyethylene, polypropylene, a polypropylenecopolymer, or others.

In anticipation that such a coating could be developed (core-shellpolymerization technology is well known in the art), the potential“core” of this hypothetical particle was evaluated by making use ofcommercially available ethylene copolymers in pelletized form. Suchcopolymers could conceivably be pulverized and subsequently coated, or adifferent polymerization process could be employed to produce coreparticles with non-permeable shells. For the purposes of thisevaluation, the pelletized copolymers, Elvax 4355, and Nucrel 3990, wereused as received, and were melt blended into formulations via proceduresoutlined in Examples 1 and 2. In order to test the potential shelfstability (if they were to exist as small particle particulates), thepolymer pellets were placed into separate glass vials at a 1/1-weightratio of mineral oil to polymer. The vials were placed into an oven setat 50° C., and were removed after overnight exposure. The samples wereallowed to cool to room temperature, and were then evaluated forgelation. The Elvax 4355 pellets (25% VA, 0.7 to 1.4% MA) werecompletely gelled with one another, whereas the Nucrel 3990 (9% MA)pellets were still free flowing. This result was consistent with earlierobservations that showed the detrimental effect of higher vinyl acetatelevels on shelf storage stability.

Formulations were prepared with 4.5 g of each pelletized polymer, 2.0 gof E43P maleated polypropylene, 0.7 g sebacic acid, and 4 g of mineraloil. Table 15 shows the results for paper adhesion, and 24-hourexudation evaluations for the two comparative formulations.

TABLE 15 Comparative Paper Adhesion and Exudation of Formulations MadeWith Nucrel 3990 and Elvax 4355 Formulation Paper Adhesion (#pass/5) 24Hour Exudation 9-1 5/5 None 9-2 1/5 Slight

These data show that high VA content ethylene copolymers produce goodfinished adhesives, whereas ethylene copolymers with little to no vinylacetate content yield poor results with mineral oil as the liquid phase.On the other hand, the shelf stability in a mineral oil liquid phasebecomes increasingly better with lower vinyl acetate levels. Thus, incombination with the data of previous examples, this example shows thatdesirable end-use properties (with a mineral oil liquid phase) can onlybe achieved when the VA content of the reinforcing phase copolymer isgreater than zero, and less than 18% (see example 3). In the absence ofVA, poor properties are observed, and when the VA content is too high,shelf stability suffers. In cases where higher vinyl acetate copolymersare desired for their good adhesive attributes, such particles should becoated with non-adsorbing polymers like polyethylene-co-methacrylic acid(i.e., something like the Nucrel 3990 of this example).

Example 10

This example demonstrates the possibility of using a different adsorbentphase (polycaprolactone) and a different liquid phase (dibutylphthalate)to produce a shelf-stable liquid dispersion that could be fused to forma non-exuding, solid product. Unlike formulations prepared withpolypropylene-co-maleic anhydride and mineral oil, the formulations inthis example were found to exhibit low levels of adhesion to paper.However, the results still demonstrate the broad scope of the invention:namely, stable, non-exuding solids can be fused from liquid dispersionswhen the appropriate adsorbent phase and liquid phase are chosen.

The efficiency of polycaprolactone (Capa 6501) as an adsorbent phase wasfirst tested by melt blending it with various potential liquid phasematerials (at a 1/1-weight ratio) including methyloleate,glyceroldioleate, epoxidized soy oil, mineral oil, and dibutylphthalate.Each mixture was melt-blended at 385° F., and was then allowed to coolon aluminum foil at room temperature. Exudation was monitored after 24hours. Out of the five liquids tested, only the Capa 6501/DBP blendshowed no exudation. Next, a formulation was prepared with 3.5 g FE532EVA, 3.0 g Capa 6501, 0.7 g sebacic acid, and 4.5 g DBP. A similarformulation was prepared using 4 g FE532 EVA, 2.5 g Capa 6501, 0.7 gsebacic acid, and 4.5 g DBP. Unlike analogous formulations prepared withE43P and phthalate esters, the finished adhesives with Capa/DBP producedno exudation. However, they were cohesively weaker (qualitatively).Also, unlike E43/mineral oil formulations, the Capa/DBP formulations didnot adhere to paper stock.

Although the adhesion properties of these formulations werecomparatively worse than those of analogous E43P and mineral oilformulations, this example nevertheless shows that alternativeadsorbent/liquid phases can be employed to produce fusible solids withlow exudation. In this particular case, Capa prevents exudation of DBPwhich otherwise exudes from EVA (see Example 1, Sample 1-10). Thus, itis conceivable that a variety of liquids could be employed as long as anappropriate adsorbent phase is identified. Furthermore, physicalproperties could be improved by using a liquid and/or polymer withreactive functionality (together with appropriate catalysts).

As a final note, this example also serves to further demonstrate thesurprising uniqueness of E43P/mineral oil formulations. Namely, eventhough both Capa/DBP and E43P/mineral oil formulations do not exude,only the E43P/mineral oil formulations provide excellent adhesion topaper stock. Thus, minimal exudation is not in itself a guarantee ofgood adhesion.

Example 11

This example demonstrates the effect of nanoparticles on the heatdistortion temperature, as judged by the upper temperature for cohesivefailure of paper stock, and the relative adhesive stiffness. The examplealso demonstrates the sensitivity of end-use performance to the methodby which the mixture is processed. The formulations for this examplewere melt blended with a spatula over a hot plate for 1 minute at 385°F., and were then tested for both exudation and paper adhesion (viamethods and procedures outlined in prior examples). Paper adhesion wasalso evaluated at elevated temperatures by allowing coupons toequilibrate for 30 minutes in an oven at various preset temperaturesprior to tear testing.

The nanoparticle material for this example was Nanomer I-44montmorillonite from Nanocor. The nanoparticles were incorporated in oneof two ways: they were either directly added to the formulation (intheir aggregated form as-received); or they were pre-blended to form amineral oil/nanoparticle concentrate, which was then subsequentlydiluted into the formulation at the appropriate level. Mineraloil/nanoparticle concentrates were prepared by blending 70/30 ratios ofoil to powder in a small Hobart mixer. Simple stirring of the 70/30mixture produced a low viscosity slurry. However, high intensityblending with the Hobart mixer provided the shear required to at leastpartially exfoliate the aggregated particles, as evidenced by theformation of a high viscosity gel. This gel was then diluted into thefinished formulation with simple low shear stirring (using a hand heldspatula) to produce a pourable liquid dispersion with the desired levelof Nanomer I-44.

Qualitative comparisons of formulations prepared by direct addition ofnanoparticles vs. those prepared with the addition of a premixedconcentrate showed that little to no improvement in stiffness or upperadhesion temperature was achieved through direct addition. Propertyimprovements were only achieved when premixed concentrate was employed.This result shows that sufficient shear is required to exfoliate theparticles so that end use property improvements can be realized. Thus,the end-use performance of these adhesives is surprisingly sensitive tothe process by which they are made.

Table 16 shows four comparative formulations, and Tables 17 and 18respectively show the results of paper tear adhesion evaluations vs.temperature (# pass out of 6), and the relative stiffness of each sampleat room temperature (1=low, 4=high).

TABLE 16 Nanoparticle Formuations for Example 11 Ingredient 11-1 11-211-3 11-4 FE532 EVA 4.5 4.5 4.5 4.5 E43P 2.0 2.0 2.0 1.8 Sebacic acid0.6 0.6 0.6 0.6 Drakeol 10 mineral oil 4.4 5.4 4.4 4.4 Nanomer I-44(direct addition) 0 0.45 0 0 70/30 mineral oil/Nanomer I-44 0 0 1.5 1.0concentrate

TABLE 17 Paper Tear Adhesion vs. Temperature of NanoparticleFormulations Temperature for Paper Tear Adhesion Test (° F.) 11-1 11-211-3 11-4 70 6/6 6/6 6/6 6/6 110 6/6 6/6 6/6 6/6 120 6/6 6/6 6/6 6/6 1303/6 3/6 6/6 6/6 135 3/6 3/6 6/6 6/6 140 3/6 3/6 3/6 3/6

TABLE 18 Relative Stiffness (at room temperature) of NanoparticleFormulations Formulation Relative Stiffness (1 = low, 4 = high) 11-1 111-2 2 11-3 3 11-4 4

These results show that when properly exfoliated, the nanoparticlesincrease both the stiffness of the adhesive, and the upper temperaturelimit for achieving cohesive paper tear. Even though the adjustedmineral oil level is the same for 11-2 and 11-3, the properties are onlyimproved when the exfoliated concentrate is employed. Also, the control(11-1) exhibits worse properties than 11-3 in spite of 11-3's highermineral oil level. Example 6 showed that higher mineral oil levelsgenerally result in worse properties. However, this example shows thatnanoparticles can improve material properties enough to compensate forthe elevated level of mineral oil. Thus, in addition to all of its otherbenefits, this invention provides a method by which nanoparticles can beexfoliated and subsequently incorporated into fusible liquidformulations to produce adhesives with substantial propertyimprovements.

Example 12

This example further demonstrates the sensitivity of end-use performanceto the method by which the nanocomposites are processed. Theformulations for this example were melt blended with a spatula over ahot plate at 385° F. for a specified time, and were then tested for bothexudation and paper adhesion (via methods and procedures outlined inprior examples). Paper adhesion was also evaluated at elevatedtemperatures by allowing coupons to equilibrate for 30 minutes in anoven at various preset temperatures prior to tear testing.

The nanoparticle material for this example was Nanomer I-44montmorillonite from Nanocor. The nanoparticles were incorporated in oneof two ways. In sample 12-1, they were directly added “as-received” tothe formulation (in their aggregated form). For the case of sample 12-2,mineral oil/nanoparticle concentrates were first prepared by blending70/30 ratios of oil to powder in a small Hobart mixer. As noted inExample 11, simple stirring of the 70/30 mixture produced a lowviscosity slurry. High intensity blending with the Hobart mixer providedthe shear required to exfoliate the aggregated particles, as evidencedby the formation of a high viscosity gel. Using simple low shearstirring (with a hand held spatula), the concentrated gel was thendiluted into neat mineral oil (minus the other ingredients). Theresultant low viscosity dispersion of Nanomer I-44 in oil was thenexposed to an ultrasound bath for one hour in an attempt to furtherexfoliate the nanoparticles. Upon removal from the ultrasound bath, theNanomer I-44/oil mixture was observed to be a translucent gel,indicative of a higher degree of exfoliation than was achieved with asimilar sample, 11-3. At this point, the remainder of the formulationingredients was added to yield a gelled version of the adhesive, withotherwise the same composition as sample 12-1. Thus, the dispersionsdiffered only in the methods used to prepare them. The ingredients inboth 12-1 and 12-2 were as follows: FE 532 EVA, 4.5 g (35.9%), E43P, 2.0g (16.0%), Sebacic acid, 0.7 g (5.6%), Mineral oil, 5.0 g (39.9%), andNanomer I-44, 0.32 g (2.6%).

Samples 12-1 and 12-2 were hot plate blended for one minute at 385° F.(with the usual one minute pre-heat period). In addition, a secondaliquot of sample 12-1 was hot plate blended (with rigorous stirring)until the degree of translucency was qualitatively equivalent to thetranslucency of sample 12-2 (approximately five minutes of mixing timewas required). Thus, the hot-melts differed only in the time and shearapplied during blending. Table 19 provides a summary of the comparisons.Table 20 compares the adhesion results at room temperature and at asubstrate temperature of 140° F.

TABLE 19 Comparison of Methods Used to Process Nanomer I-44 inComparative Samples From Example 12 Qualitative Method of Method ofDispersion State Evaluation of Hotmelt Sample Mixing Dispersion Blending12-1A Direct addition; low shear Low viscosity 1 minute of mixing liquidshear, 385° F. dispersion 12-1B Direct addition; low shear Low viscosity5 + minutes mixing liquid of shear at dispersion 385° F. to achieveimproved translucency 12-2 Addition of 70/30 High viscosity 1 minute ofexfoliated concentrate to gel shear, 385° F. oil only; low shear mixing;ultrasound; remainder of ingredients added with low shear

TABLE 20 Paper Tear Adhesion Results at Room Temperature and at aSubstrate Temperature of 140° F. (# Pass out of 5) Sample 70° F. 140° F.12-1A 5/5 2/5 12-1B 5/5 5/5 12-2 5/5 5/5

These results show that elevated temperature adhesion characteristicsare improved as the degree of exfoliation increases. These results alsodemonstrate the unique viscosity control feature of this invention.Namely, dispersions with otherwise identical compositions can be madewith rheological characteristics ranging from those of a liquid (theaggregate-dispersion form of the invention) to those of a high viscositygel or paste (the pre-exfoliated form of the invention). Hence, there isa great deal of latitude for process control. For example, a gel orpaste could be useful in a continuous application process where it isimportant to maintain a bond-line during the working period between anadhesive's application, and its final “cure.” A gel or paste could alsobe useful in a caulking application where a continuous bead is to beapplied, and then heated to achieve final fusion. At the other extreme,the aggregate dispersion form of this invention enables the use ofsimple processing equipment for low viscosity liquids. Subsequent shearcan then be applied during the stage of molten hot-melt mixing toachieve adequate exfoliation, together with adequate mixing of thereinforcing and adsorbent phases of the dispersion. Also, anyintermediate stage (i.e., partial pre-exfoliation) could also be useful,as was accomplished with sample 11-3 in Example 11.

In yet another aspect of this invention, the nanoparticle aggregatescould be added directly to any hot melt-adhesive formulation (either theconventional solid-types or the novel hybrid types of this invention)with the objective of postponing the exfoliation step until the pelletsor liquids are subjected to the final process of application to apackaging substrate. In this way, the process costs associated withpre-exfoliation could be minimized, and the benefits of nanocompositeenhancement could be achieved by subjecting the adhesives to sufficientshear during the process of applying the adhesive to a substrate.

Example 13

Formulations were made for the purpose of determining the effect ofreinforcing phase molecular weight and vinyl acetate level on adhesion.All formulations were prepared with 4.5 g of the reinforcing phasepolymer, 2.0 g E43P adsorbent phase, 0.7 g sebacic acid activator, and5.0 g mineral oil. The procedures for mixing were the same as thosereported in Examples 1 and 2. Paper tear coupons were also made asdescribed in prior examples. Paper tear adhesion was tested as afunction of substrate temperature using the procedures as outlined inExamples 11 and 12. Comparative polymers for this example are listed inTable 21. The results of paper tear adhesion vs. temperature areprovided in Table 22.

TABLE 21 Comparative Poly(ethylene-co-vinyl acetate) Reinforcing PhasePolymers for Example 13 Formulations Sample Polymer Melt Index % VA 13-1EVA-1 3 9 13-2 EVA-2 3 12 13-3 EVA-3 3 15 13-4 FE532 EVA 9.5 9

TABLE 22 Paper Tear Adhesion vs. Temperature for Example 13 Formulations(Percentage of passing samples out of eight) Temperature for Paper TearAdhesion Test (° F.) 13-1 13-2 13-3 13-4 72 100 100 100 100 120 100 100100 100 130 100 75 75 100 140 100 50 0 50 150 75 0 0 0

These results illustrate several important aspects of this invention.First, an increase in the molecular weight of the reinforcing phase(compare samples 13-1 and 13-4) leads to improved adhesion at elevatedtemperatures. Thus, the preferred molecular weight of the reinforcingphase will depend on the desired end-use temperature range, as well asthe desired melt-process characteristics (the viscosity of the moltenstate will increase with increasing molecular weight). Secondly, anincrease in the VA % at an otherwise constant molecular weight leads toa decrease in the upper adhesion temperature. Thus, the preferred VAcontent will also depend on the desired end-use temperature range, aswell as the desired melt-process characteristics (the viscosity of themolten state will generally decrease with increasing VA content). Asshown in prior examples, the upper VA limit is also dependent on thedesired storage temperature characteristics for the liquid dispersion(higher VA level leads to a lower storage temperature limit for reasonsrelated to gelation). It can also be appreciated from prior examplesthat the heat distortion temperature and hence the upper temperatureadhesion threshold can be increased through the incorporation ofnanoparticles—independent of molecular weight and VA content. Thus, whentaken in combination, the embodiments of this invention provide thecapability to produce adhesives with a wide range of processing andend-use characteristics.

Example 14

Formulations were prepared for the purpose of illustrating the utilityof an adsorbent phase comprised of a blend of polypropylene homopolymerand maleated polypropylene. The results of show that little to noadhesion is achieved when the adsorbent phase is comprised ofpolypropylene homopolymer. However, when maleated PP is blended with PPto form the adsorbent phase, acceptable adhesion is achieved. Thisresult shows that the preferred adhesive is one where the adsorbentphase is comprised of maleated PP, or PP blended with maleated PP. Theformulations for this example were made and tested in accordance withthe aforementioned procedures. The formulations and results are providedin Table 23.

TABLE 23 Ingredients, Paper Tear Adhesion Results, and Visual ExudationEvaluations for Example 14 Formulations Ingredient 14-1 14-2 14-3Equistar FE 532 EVA 4.5 4.5 4.5 Honeywell E-C 597 A Maleated PP 2.0 00.6 A-CX Grade 2440 Polypropylene Wax 0 2.0 1.4 Sebacic Acid 0.7 0.7 0.7Mineral Oil 5.0 5.0 5.0 Paper Tear Adhesion (# pass out of 5 2 5 fivecoupons) Exudation (after three days) None Partial None

Example 15

The purpose of this example is to demonstrate that density reduction canbe achieved through the incorporation of foaming agents. When hot-meltadhesives are dispensed as a cellular foam, they provide significanteconomical advantages by decreasing the mass of adhesive required toobtain any given adhesive bead volume or dimension. For example, adding30% gas by volume to a given hot-melt will decrease its mass by the sameamount; therefore decreasing the cost per bead by the same amount.

Since conventional hot-melts are manufactured and processed attemperatures above the decomposition temperatures of manychemical-blowing agents, it is not possible to use foaming agents toachieve a cellular foamed structure. Instead, a relatively costlyprocess modification is required, whereby gas is mechanically added tothe molten hot-melt, and is then dissolved into the molten liquid whileunder pressure. When the adhesive is dispensed to atmospheric pressure,the solvated gas expands to create a hot-melt foam. Nordson Corporationof Amherst, Ohio offers equipment for this purpose.

The liquid plastisol nature of the present invention facilitates foamingwithout the use of expensive equipment modifications. Thus, process andmaterial costs can be readily achieved. In order to illustrate this,formulation 15-1 in Table 24 was mixed by hand to form stable liquidplastisol at room temperature.

TABLE 24 Example 15 Formulation 15-1 Ingredient Parts By Weight EquistarFE 532-EVA 4.5 Eastman E43P Maleated PP 2.0 Sebacic Acid 0.7 Celogen 754(blowing agent with catalyst) 0.09 Mineral Oil (Penrico D35) 5.0

Formulation 15-1 was pumped under pressure from its ambient containerthrough a heat exchanger to elevate its temperature to 350° F. Theliquid became molten as it passed through the heater. Viscous drag inthe heater provided adequate shear for mixing the polymer blend to forma homogeneous melt. Simultaneously, the chemical blowing agentdecomposed to liberate nitrogen gas into the molten adhesive. The gasremained solvated at a pressure of 300 psi.

Solvation of the gas was audibly detected as the molten liquid wasdispensed to atmospheric pressure. When the gas was incompletelysolvated, audible crackling and hissing sounds were observed to emanatefrom the dispensing nozzle tip. Crackling sounds were readily observedat 100 psi, and the audible level was observed to gradually decreaseuntil no sound could be heard at 300 psi. When dispensed at 300 psi, theextruded material was observed to expand to form a closed cell foam. At100 psi, the formulation did not foam, and at 150 psi, the cellular foamstructure started to appear with relatively large combinations of openand closed cells. The cell structure was observed to become finer andpredominantly closed-cell in nature as the pressure approached 300 psi.At pressures of 300 psi and higher, the resulting extrudate produced afine, closed-cell foam.

When compared to an equivalent formulation without the foaming agent,the resultant 15-1 extrudate provided a density reduction ofapproximately 49%. In addition, the foamed hot-melt adhesive providedexcellent paper-tear adhesion.

In accordance with the provisions of the patent statutes, the inventionhas been described in what is considered to represent its preferredembodiments. However, it should be noted that the invention can bepracticed otherwise than as specifically illustrated and describedwithout departing from its spirit or scope.

For example, aside from providing a novel adhesive for paper, theinvention described herein provides for many additional potential uses.These uses include, but are not limited to, adhesives for othermaterials; caulking materials; sealants; gaskets; encapsulants tofacilitate controlled release of natural and synthetic products inapplications ranging from agricultural to medical applications; lowadhesion strippable protective coatings for metals and wires (as suchthey could be formulated with corrosion inhibitors); textile coatings;thermoset coatings for applications demanding abrasion resistance suchas floor tiles, wood, and furniture; wear layers for flexible sheetflooring; chemically embossable foamed layers for flexible sheetflooring; safety glass interlayers and solar cell encapsulants;injection molded parts for toys; components for consumer goods;components for industrial and automotive applications; components forconstruction applications, plumbing applications, electricalapplications; and others. In addition, both release and adheringembodiments of this invention could be formulated to serve as barriercoatings for civil and military defense applications.

1. A method of producing adhered substrates comprising: providing anadhesive composition in the form of a liquid dispersion, the liquiddispersion comprising solid particles of a first component comprising aco-polymer or a terpolymer prepared from monomers including at leastethylene and vinyl acetate and solid particles of a second componentcomprising a copolymer prepared from monomers including at leastpropylene and maleic anhydride dispersed in a third component comprisinga non-reactive hydrocarbon that is a liquid at room temperature; heatingand mixing the liquid dispersion at a temperature above about 300° F. toform a molten blend; disposing the molten blend between the substratesto be adhered to each other; and retaining the molten blend between thesubstrates to be adhered to each other for a set time during which themolten blend cools to form a solid adhesive that adheres the substratesto each other.
 2. The method according to claim 1 wherein the substratescomprise paper stock.
 3. The method according to claim 2 wherein thesolid adhesive is capable of producing fiber-tear adhesion between thepaper stock substrates.
 4. The method according to claim 1 wherein theset time not more than about two seconds.
 5. The method according toclaim 1 wherein the first component comprises a poly(ethylene-co-vinylacetate) copolymer, a poly(ethylene-co-vinyl acetate-co-methacrylicacid)terpolymer, a poly(ethylene-co-vinyl acetate-co-maleicanhydride)terpolymer or a mixture thereof.
 6. The method according toclaim 1 wherein the second component comprises apoly(propylene-co-maleic anhydride) copolymer.
 7. The method accordingto claim 6 wherein the poly(propylene-co-maleic anhydride) copolymer isblended with a polypropylene homopolymer, a rosin ester ofpentaerythritol or a mixture thereof.
 8. The method according to claim 1wherein the third component comprises mineral oil, vegetable oil or amixture thereof.
 9. The method according to claim 1 wherein the adhesivecomposition further comprises one or more tackifiers selected from thegroup consisting of terpene resins, rosin ester derivatives andhydrocarbon-based derivatives.
 10. The method according to claim 9wherein the one or more tackifiers is blended with the second componentor dissolved in the third component.
 11. The method according to claim 1wherein: the first component comprises a poly(ethylene-co-vinyl acetate)copolymer, a poly(ethylene-co-vinyl acetate-co-methacrylicacid)terpolymer, a poly(ethylene-co-vinyl acetate-co-maleicanhydride)terpolymer or a mixture thereof; the second componentcomprises a poly(propylene-co-maleic anhydride) copolymer; and the thirdcomponent comprises mineral oil, vegetable oil or a mixture thereof. 12.The method according to claim 11 wherein the poly(propylene-co-maleicanhydride) copolymer is blended with a polypropylene homopolymer, arosin ester of pentaerythritol or a mixture thereof.
 13. The methodaccording to claim 11 further comprising an activator comprising adicarboxylic acid selected from the group consisting of sebacic acid anddodecanedioic acid.
 14. The method according to claim 11 furthercomprising a heat-activated blowing agent and/or calcium carbonate. 15.The method according to claim 11 further comprising nanoparticleaggregates.
 16. The method according to claim 15 wherein thenanoparticle aggregates become exfoliated when the liquid dispersion isheated above about 300° F. and mixed.
 17. A method of producing adheredsubstrates comprising: providing an adhesive composition in the form ofa liquid dispersion, the liquid dispersion comprising solid particles ofa first component comprising a polymeric adhesive material that is asolid at room temperature and solid particles of a second component thatis a different material than the first component and is a solid at roomtemperature dispersed in a third component that is a liquid at roomtemperature; heating and mixing the liquid dispersion at a temperatureabove about 300° F. to form a molten blend; disposing the molten blendbetween the substrates to be adhered to each other; and retaining themolten blend between the substrates to be adhered to each other for aset time during which the molten blend cools to form a solid adhesivethat adheres the substrates to each other, wherein the second componentsubstantially minimizes exuding of the liquid from the solid adhesive.18. The method according to claim 17 wherein the substrates comprisepaper stock.
 19. The method according to claim 18 wherein the solidadhesive is capable of producing fiber-tear adhesion between the paperstock substrates.
 20. The method according to claim 17 wherein the settime not more than about two seconds.
 21. The method according to claim17 wherein the first component is at least partially incompatible withthe third component when the adhesive composition is in the form of thesolid adhesive.
 22. The method according to claim 17 wherein the secondcomponent is compatible with the third component when the adhesivecomposition is in the form of the solid adhesive.
 23. A method ofproducing adhered substrates comprising: providing a non-PVC adhesivecomposition that is a liquid dispersion when stored at temperatures fromabout room temperature up to about 140° F., becomes a molten solutionwhen heated to a temperature above about 300° F. and mixed, and thenbecomes a non-exuding thermoplastic solid adhesive upon cooling below atemperature of about 140° F.; heating and mixing the liquid dispersionat a temperature above about 300° F. to form the molten blend; disposingthe molten blend between the substrates to be adhered to each other; andretaining the molten blend between the substrates to be adhered to eachother for a set time during which the molten blend cools to form thesolid adhesive that adheres the substrates to each other.
 24. The methodaccording to claim 23 wherein the solid adhesive is capable of producingfiber-tear adhesion between paper stock substrates that are adhered toeach other by the solid adhesive.
 25. A method of producing adheredsubstrates comprising: providing an adhesive composition comprising afirst component comprising a polymeric material that is a solid at roomtemperature, a second component that is a different material than thefirst component and is a solid at room temperature, and a thirdcomponent that is a liquid at room temperature, wherein the adhesivecomposition is in the form of: a liquid dispersion when stored attemperatures from room temperature up to about 140° F., the liquiddispersion comprising discrete solid particles of the first componentand discrete solid particles of the second component dispersed in thethird component, a molten blend when heated above about 300° F. andmixed, and a solid adhesive when the molten blend cools to a temperaturebelow about 140° F., the solid adhesive being characterized by the firstcomponent being at least partially incompatible with the thirdcomponent, and the second component being compatible with the thirdcomponent; heating and mixing the liquid dispersion at a temperatureabove about 300° F. to form the molten blend; disposing the molten blendbetween the substrates to be adhered to each other; and retaining themolten blend between the substrates to be adhered to each other for aset time during which the molten blend cools to form the solid adhesivethat adheres the substrates to each other.